The idea of engineering a virus that selectively kills cancer cells has been around for at least a decade, but it's only in the past year or two that this dream has begun to reach fruition. A spate of new studies suggest the approach is one of the most promising recent developments in the war on cancer.

In a trial of 14 patients with advanced liver cancer (usual treatment options had been exhausted and they were expected to live only a few more months), a genetically altered virus slowed cancer progression in all but four volunteers. Three patients survived more than 15 months after the virus was injected, says David Kirn, MD, CEO of Jennerex Biotherapeutics in San Francisco, lead author on the study. Next he plans to test the virus against breast, lung, neck, and head cancers.

Doctors at the University of Texas M.D. Anderson Cancer Center in Houston have customized an adenovirus—it causes colds—to attack the cells of glioblastoma, the most common, aggressive, and deadly type of brain tumor. In a study published in the Journal of the National Cancer Institute, they showed that, in mice, the virus is able not only to kill glioblastoma cells but also destroy the stem cells that initiate the cancer's growth. "Thirty percent of the tumors in the mice disappeared with this method after chemotherapy and radiation had had no effect," says Frederick Lang, MD, co–senior author of the study and director of clinical research at the center. Testing in patients, he says, is expected to begin this summer.

Mayo Clinic researchers believe they may have come up with a method to deliver a virus that can prevent cancer's spread throughout the body. Because cancer cells travel via lymph nodes, the researchers loaded their virus onto T-cells, immune cells that use the same pathway. In nearly all the mice, tumors disappeared. Even more remarkable, when the researchers injected the cured mice with the cancer again, their immune system recognized and disposed of the cells. "The immunity lasted the life of the mice, so our hope is that we'll find that it does the same in people," says Richard Vile, PhD, professor of novel therapeutics at the clinic and lead researcher of the study. Human trials are expected to begin in the next year, he says.

Still, it's early in the process, warns Margaret Offermann, MD, PhD, deputy national vice president for research at the American Cancer Society. "The results are promising, but cancers are pretty clever." Until there is more research, drugs, radiation, and surgery techniques remain our best response.